Direct-drive Synchronous Generator Research Articles

Comparison of designs of synchronous machines with integrated torque transformer for renewable energy

Increasing the specific torque of electric machines is an urgent problem for a number of low-speed power electromechanical systems, one of such systems is a wind power plant. Determining the optimal design of a synchronous generator with a built-in torque transformer is important for the further development of wind power. The purpose of the research is to determine the optimal design of a generator with a built-in torque transformer for wind power plants, which is a solution to the problem of creating low-speed, high-torque and relatively compact electric generators, and will make it possible to abandon the gear drive. The paper examines two designs of a direct drive synchronous generator with a built-in torque transformer with two and three air gaps. The calculation is performed using the Comsol Multiphysics software based on the finite element method. The main criteria for comparison are the generator's output power, the maximum torque of the low-speed rotor connected to the wind turbine, the maximum torque per unit volume of the generator, and the maximum torque per unit mass of the permanent magnets. Based on the calculation results, it has been concluded that a synchronous generator with two air gaps has a higher torque per unit volume and torque per mass of permanent magnets, i. e. with the same power, the expenses on active materials will be lower. This type of generator has a higher output power compared to both the direct-drive synchronous generator and the synchronous generator with three air gaps, with the same dimensional parameters.

A Study of Dynamic Equivalence Method for Multiple Wind Farms in Urban Power Grids

As the number of wind farms (WFs) in urban power grids gradually increases, their dynamic equivalence is needed for stability analysis. This paper proposes a dynamic equivalence method for distributed multiple wind farms in an urban power grid. The key idea is to characterize wind farms dynamics and then use them for coherence by considering the differences between doubly-fed induction generators (DFIG) and permanent magnet direct-drive synchronous generators (PMSG). The mathematical-physical models and operational control characteristics are firstly analyzed to find the essential attributes representing the dynamic characteristics. Then we introduce the similarity based on the dynamic timing warping (DTW) distances, which help construct the clustering index for coherency wind farms. Meanwhile, comprehensive constraints, which ensure the consistency of the urban power grid topology, are adequately considered. Finally, the parameters of coherent wind farms are aggregated based on the clustering groups. The proposed method is validated in an urban grid by the time-domain simulation.

Comparative life cycle assessment of electricity generation by different wind turbine types

Wind turbines produce electricity with hardly any emissions during operation. Most environmental impacts are associated with their manufacture. This work performs a comparative life cycle assessment (LCA) to evaluate the environmental impacts of different 3 MW power class wind turbines at a fictive onshore site in Germany. The three most frequently installed onshore turbine types are considered: geared converter with doubly-fed induction generator (DFIG), direct driven synchronous generator (DDSG) electrically excited and direct drive permanent magnet synchronous generator (DDPMSG). LCA reveals that environmental impacts are concentrated during manufacturing of fundament, tower and nacelle, which account for up to 19%, 30% and 99% of single impacts, respectively. Main drivers are the use of copper, steel and in case of DDPMSG also the rare earth permanent magnets. The DDSG shows higher impacts than the other wind turbines in 14 out of all 15 categories, due to the higher weight of its nacelle. Impacts due to operation add up to 3%.Four sensitivity analyses are conducted to estimate the effects of component replacement, recycling, origin of rare earths for permanent magnet production for DDPMSG and electricity yield. Possible recycling options show the highest improvement potential and even change turbine types ranking.

Wind turbine blade geometry design based on multi-objective optimization using metaheuristics

The application of evolutionary algorithms to wind turbine blade design can be interesting, by reducing the number of aerodynamic-to-structural design loops in the conventional design process, hence reducing the design time and cost. Recent developments showed satisfactory results with this approach, mostly combining genetic algorithms with the blade element momentum theory. The general objective of the present work is to define and evaluate a design methodology for the rotor blade geometry in order to maximize the energy production of wind turbines and minimize the mass of the blade itself, using for that purpose stochastic multi-objective optimization methods. An optimization benchmark problem was proposed, which represents the wind conditions and present wind turbine concepts found in Brazil. A variable speed pitch-controlled 2.5 MW direct-drive synchronous generator turbine with a rotor diameter of 120 m was chosen as concept. Four different multi-objective evolutionary algorithms were selected for evaluation in solving this benchmark problem: Non-dominated Sorting Genetic Algorithm version II (NSGA-II), Quantum-inspired Multi-objective Evolutionary Algorithm (QMEA), Multi-objective Evolutionary Algorithm Based on Decomposition (MOEA/D), and Multi-objective Optimization Differential Evolution Algorithm (MODE). Detailed analysis of the best compromise blade design showed that the output of the design methodology is feasible for manufacturing.

Dynamic Modeling and Controller Design for a Novel Front-End Speed Regulation (FESR) Wind Turbine

Most existing wind turbine generation systems (WTGS) are based on double-fed induction generator (DFIG) and direct-drive synchronous generator (DDSG). In this paper, we investigate the modeling and controller design of a novel front-end speed regulation (FESR) wind turbine with differential variable ratio gearbox (VRG). For this wind turbine, a surface mount permanent magnet synchronous motor (SPMSM) unit is embedded to maintain the constant (i.e., synchronous) speed of the generator shaft over wide range of wind speed, which allows the conventional synchronous generator to be used to construct a grid-friendly WTGS. Compared with DFIG and DDSG, the novel FESR does not use converters for grid-connecting but adopt SPMSM to ensure the synchronous speed. A model-independent speed control algorithm for maximum power point tracking (MPPT) is developed based on a neuro-adaptive backstepping approach. Theoretical analysis and numerical simulations show that the proposed control scheme ensures more precise motor speed tracking in the presence of parameter uncertainties and external load disturbances.

Power Extraction Control of Variable Speed Wind Turbine Systems Based on Direct Drive Synchronous Generator in All Operating Regimes

Due to the increased penetration of wind energy into the electrical power systems in recent years, the turbine controls are actively occupied in the research. This paper presents a nonlinear backstepping strategy to control the generators and the grid sides of a Wind Farm System (WFS) based Direct Drive Synchronous Generator (DDSG). The control objectives such as Tracking the Maximum Power (TMP) from the WFS, pitch control, regulation of dc-link voltage, and reactive and active power generation at varying wind velocity are included. To validate the proposed control strategy, simulation results for 6-MW-DDSG based Wind Farm System are carried out by MATLAB-Simulink. Performance comparison and evaluation with Vector Oriented Control (VOC) are provided under a wide range of functioning conditions, three-phase voltage dips, and the probable occurrence of uncertainties. The proposed control strategy offers remarkable characteristics such as excellent dynamic and steady state performance under varying wind speed and robustness to parametric variations in the WFS and under severe faults of grid voltage.

A Novel Vernier Reluctance Fully Superconducting Direct Drive Synchronous Generator With Concentrated Windings for Wind Power Application

In this paper, a novel vernier reluctance fully superconducting (FSC) low-speed direct-drive synchronous generator for a wind power application is proposed. The proposed superconducting (SC) generator is with an external rotor, and both the SC armature and SC dc field windings are in the inner stationary stator. Thus, compared with the existing FSC synchronous generators (FSCSGs), the slip ring is removed, and the cryostat and related refrigerate systems are stationary and greatly simplified. In addition, both the field and armature windings are single tooth-wound concentrated windings with very short end-windings. Compared with the regular FSCSGs, the usage of the SC material is greatly reduced in this proposed topology, as with the total cost. Furthermore, the torque ripple is much lower than that in a regular FSCSG. All these features are evaluated by the finite-element simulations.

Life-Cycle Assessment Comparison Between 15-MW Second-Generation High-Temperature Superconductor and Permanent-Magnet Direct-Drive Synchronous Generators for Offshore Wind Energy Applications

Wind energy is the world's fastest growing energy source. Specifically in the recent decade, offshore wind energy is the technology that has developed the fastest due to the stronger and stable winds produced at sea and the huge areas where it can be employed. Electricity production from wind sources has seen high growth along with wind turbine capacity, foreseeing a linear evolution in the next decade. Additionally, it has been well demonstrated recently that the larger the power per wind turbine unit installed, the lower the levelized cost of energy. Second-generation high-temperature superconductor synchronous generators with direct-drive technology (2GHTSDDSG) for offshore wind energy applications have recently emerged as an alternative to consider instead of permanent-magnet direct-drive synchronous generators (PMDDSG), due to their lower dimensions and low weight per megawatt. This paper contains a detailed “cradle-to-gate” life-cycle assessment of the 15-MW 2GHTSDDSG and PMDDSG, using GaBi 6 commercial software and PE International Professional and Ecoinvent 2.2 databases, as a result of quantifying each component required for the production. After a detailed inspection of each component fabrication, conclusions and recommendations are obtained and presented.

Effect of high-voltage direct current link on small signal stability of a power system with different penetration level of doubly fed induction generator and direct drive synchronous generator based wind farms

ABSTRACTHigh penetration level of wind power has significant impact on the dynamic performance of power system. Power system with existing high-voltage direct current (HVDC) link may influence the stability of power system at high penetration level of wind power. This article investigates the stability issues of power system with existing HVDC link for different penetration level of doubly fed induction generator (DFIG) and direct drive synchronous generator (DDSG) based wind farms. The small signal stability analysis shows that power system with HVDC link has improved the stability of the power system for increased penetration of DFIG- and DDSG-based wind farms.

Voltage Stability Enhancement using VSWT with Direct Drive Synchronous Generators

Th is paper investigates about the enhancement in grid voltage stability while integrating the large-scale variable speed wind turbine (VSWT) with direct drive synchronous generators (DDSG). A dynamic modeling and simulat ion of a grid connected VSWT driven DDSG with controllable power inverter strategies suitable for the study was developed, tested and verified. Th is dynamic model with its control scheme can regulate real power, maintain reactive power and generate voltage at different wind speeds. For th is paper, studies were conducted on a standard IEEE 14 bus system augmented by a rad ially connected wind power p lant (WPP) which contains 100 wind turbine generators (WTG). The studies include examin ing the voltage stability (λ-V) curves, voltage magnitude, reactive power delivered, loading margin and voltage collapse of the system. These voltage stability studies are done for the normal state as well as for line contingencies. It is found that large scale VSWT with DDSG at the transmission level has the potential to imp rove the long-term voltage stability of the grid by injecting react ive power with the help of controllable power inverter strategy.

Direct-Drive Synchronous Generators with Excitation from Strontium-Ferrite Magnets: Efficiency Improvement

Direct-Drive Synchronous Generators with Excitation from Strontium-Ferrite Magnets: Efficiency Improvement The authors consider the possibility to raise the specific power of synchronous generators with excitation from inexpensive permanent magnets. For this purpose, it is proposed to use tooth-wise windings and permanent magnets based on inexpensive magneto-hard material, e.g. strontium-ferrite. The magnets are to be placed between the rotor teeth, the alternate polarity of which is facing the air-gap. This provides a simpler and cheaper technology of making such a generator and improves its reliability. The proposed rational bevelling of the stator teeth not only raises the specific power of the generator but also reduces the level of noise and vibrations, extends the longevity of the magnets and bearings as well as facilitates the starting torque of the electric machine, e.g. if it is employed as wind generator.

Coordinated utilisation of wind farm reactive power capability for system loss optimisation

Most wind farms currently being installed are based upon doubly fed induction generator (DFIG) or direct-drive synchronous generator (DDSG) technology. Given that one of the impacts of introducing distributed generation is an alteration of steady-state power flows and voltages, both technologies are capable of providing local voltage support. Wind farms may, therefore, be included in optimal power flow (OPF) calculations to minimise fuel cost and/or network losses. The IEEE 30-bus system is considered as a case study, comparing fixed-speed induction generator (FSIG) requirements with DFIG capability. Results are presented for a range of DFIG capability modes, at varying system load and wind farm penetration levels. A significant reduction in losses can be achieved by suitable co-ordination of DFIG reactive power import/export, operating within typical grid code specifications. It is shown that the dynamic variability of reactive power requirements is readily accommodated by the power system. Finally, implementation options for the scheme and incentivising strategies are considered. Copyright © 2010 John Wiley & Sons, Ltd.

Comparison of Direct-Drive and Geared Generator Concepts for Wind Turbines

The objective of this paper is to compare five different generator systems for wind turbines, namely the doubly-fed induction generator with three-stage gearbox (DFIG3G), the direct-drive synchronous generator with electrical excitation (DDSG), the direct-drive permanent-megnet generator (DDPMG), the permanent-magnet generator with single stage gearbox (PMG1G), and the doubly-fed induction generator with single-stage gearbox (DFIG1G). The comparison is based on cost and annual energy yield for a given wind climate. The DFIG3G is a cheap solution using standard components. The DFIG1G seems the most attractive in terms of energy yield divided by cost. The DDPMG has the highest energy yield, but although it is cheaper than the DDSG, it is more expensive than the generator systems with gearbox

Time-Domain Identification of Synchronous Generator Transfer Functions

The design of a robust frequency converter controller for high dynamic performance of a synchronous generator requires an accurate dynamic model of the electromagnetic part. In this paper, a new procedure for identifying the transfer functions of Park’s dq-axis model of a synchronous generator has been developed. It will be shown that the parameters of this model can be easily identified from standstill time-domain data. The validity of the theoretical model has been verified by comparing time-domain simulations with measurements taken from the Lagerwey LW-50/750 direct-drive synchronous generator. It can be concluded that a consistent model estimate of the electromagnetic part of the LW-50/750 generator has been obtained. Ultimate validation, however, will follow after the implementation of the designed frequency converter controller in this wind turbine.